This is just a guess, & maybe not a very good one. Since the car is a '74 model, is it possible that it's a part of the seat belt interlock system that was required for a part of that model year? The govt. required the interlock to keep the car from being started until somebody sat in the seat, & then fastened the seat belt, in that order. It wasn't popular & lasted less than a year. Maybe this is a part of the logic circuit or whatever they used to make sure things were done in the proper order. If it is, I'd look for it to hook into some wiring from the pressure sensors in the seat or somewhere in the starter wiring, maybe the firewall mounted starter relay. All of these systems were also supposed to have some type of bypass button/device under the hood in case they failed. Before I met her, my wife had a '74 Dart & she said she never was able to find the bypass & that the system was a PITA!
